Hypoxia and Hypoxemia
Start with the big picture
Hypoxia means inadequate oxygen delivery to tissues; hypoxemia means reduced arterial PaO₂. Hypoxia is classified as hypoxic, anemic, ischemic, or histotoxic, reflecting different limits on oxygen availability or use. For hypoxemia, the A–a gradient helps narrow the cause: high altitude and hypoventilation are associated with a normal gradient, while diffusion impairment, V/Q mismatch, and shunt increase it. The alveolar gas equation estimates expected alveolar oxygen for comparison with measured arterial oxygen. A key clinical distinction is response to supplemental oxygen: hypoxemia due to shunt does not improve with 100% O₂, unlike V/Q mismatch.
What you'll learn
- Distinguish hypoxia from hypoxemia.
- Identify the four types of hypoxia and their underlying mechanisms.
- Use the A–a gradient to organize causes of hypoxemia.
- Explain how the alveolar gas equation supports interpretation of PaO₂.
- Contrast shunt and V/Q mismatch by response to 100% oxygen.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
